The present invention relates to wireless communications systems in general, and more particularly to optical wireless communications systems.
Medved et al., in U.S. Pat. No. 5,818,619, which is incorporated by reference for all purposes as if fully set forth herein, teach a wireless communications system for linking different parts of an optical communications network. Each part of the network is provided with one or more optical communications network interface units and with universal converter units that are optically coupled to their respective network interface units. Each universal converter unit includes an airlink transmitter, an airlink receiver, a fiber optic receiver and a fiber optic transmitter. The fiber optic receiver receives outgoing optical signals from the network interface unit and transforms these optical signals to electronic signals. These electronic signals are sent to the airlink transmitter, where these electronic signals are transformed back to optical signals and transmitted as such into free space. The airlink receiver receives optical signals that were transmitted into free space by another universal converter unit and transforms these incoming optical signals into electronic signals. These electronic signals are sent to the fiber optic transmitter, which transforms these electronic signals back to optical signals that are sent to the network interface unit via a fiber optic cable. The network interface units and the universal converter units are operated in pairs, with each member of the pair being a portion of a different optical communications network or of a different part of the same optical communications network. The airlink transmitter of each universal converter unit is aimed at the airlink receiver of the other universal converter unit to enable exchange of optical signals between the two optical communications network or between the two parts of the same optical communications network.
The wireless communications system of Medved et al. is intended for use in an optical communications network in which signals are encoded in a single carrier wavelength. Recently, optical communications networks based on dense wavelength division multiplexing (DWDM) have been introduced. In a DWDM network, several carrier wavelengths are multiplexed on the same optical fiber. The data transmission rate available using DWDM would overwhelm the electronics of the universal converter units of Medved et al. In any case, the various carrier wavelengths would have to be demultiplexed, and a separate network interface unit and universal converter unit would be needed for each carrier wavelength.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system for linking two parts of an optical communications network that are remote from each other in a way that facilitates the exchange of DWDM optical signals.
According to the present invention there is provided an optical device including: (a) a multimode optical waveguide having a proximal end and a distal end; (b) a single mode optical waveguide having a distal end; (c) a mechanism for optically coupling the distal end of the single mode optical waveguide to the proximal end of the multimode optical waveguide; and (d) imaging optics, optically coupled to the distal end of the multimode optical waveguide.
According to the present invention there is provided an optical transmitter, including: (a) a common input optical waveguide; (b) a plurality of transmitter optical waveguides, each transmitter optical waveguide having a distal end; (c) for each transmitter optical waveguide, imaging optics, optically coupled to the distal end of the each transmitter optical waveguide; and (d) a mechanism for optically coupling the common input optical waveguide to the transmitter optical waveguides.
According to the present invention there is provided an optical receiver, including: (a) a common output optical waveguide; (b) a plurality of receiver optical waveguides, each receiver optical waveguide having a distal end; (c) for each receiver optical waveguide, imaging optics, optically coupled to the distal end of the each receiver optical waveguide; and (d) a mechanism for optically coupling the common output optical waveguide to the receiver optical waveguides.
According to the present invention there is provided an optical transceiver including: (a) a transmitter optical waveguide having a distal end; (b) transmitter imaging optics, having a transmitter optical axis, optically coupled to the distal end of the transmitter optical waveguide; (c) a plurality of receiver optical waveguides, each receiver optical waveguide having a distal end; and (d) for each receiver optical waveguide, receiver imaging optics, having a receiver optical axis, optically coupled to the distal end of the each receiver optical waveguide, the transmitter optical axis and the receiver optical axes all being substantially parallel.
According to the present invention there is provided a wireless communications system, including: (a) a transmitter optical waveguide having a proximal end and a distal end; (b) transmitter imaging optics, optically coupled to the distal end of the transmitter optical waveguide; (c) at least one receiver optical waveguide having a proximal end and a distal end; (d) for each at least one receiver optical waveguide, receiver imaging optics optically coupled to the distal end of the at least one receiver optical waveguide; and (e) an optical communication network interface unit, optically coupled to the proximal ends of the transmitter optical waveguide and of the at least one receiver optical waveguide, for transmitting optical signals to the transmitter optical waveguide and for receiving optical signals from the at least one receiver optical waveguide.
According to the present invention there is provided an optical transceiver including: (a) a transmitter optical waveguide having a distal end; (b) transmitter imaging optics, having a transmitter optical axis, optically coupled to the distal end of the transmitter optical waveguide; and (c) an airlink receiver having a receiver optical axis substantially parallel to the transmitter optical axis.
According to the present invention there is provided a wireless communication system, including: (a) a transmitter optical waveguide having a proximal end and a distal end; (b) transmitter imaging optics, optically coupled to the distal end of the transmitter optical waveguide; (c) an airlink receiver; (d) a converter unit, electrically coupled to the airlink receiver; and (e) an optical communication network interface unit, optically coupled to the proximal end of the transmitter optical waveguide and to the converter unit, for transmitting optical signals to the transmitter optical waveguide and for receiving optical signals from the converter unit.
According to the present invention there is provided an optical device including: (a) an optical fiber having a distal end; and (b) a FC/APC fiber optic connector serving as a reflection-suppressing interface between the distal end and a rarefied optical medium.
According to the present invention there is provided a wireless system for transmitting wavelength-multiplexed optical signals from a first location to a second location, including: (a) an optical transmitter, at the first location, the optical transmitter including a multimode input optical waveguide for receiving the optical signals; and (b) an optical receiver, at the second location, for receiving the optical signals from the optical transmitter.
According to the present invention there is provided a method for exchanging optical signals between two parts of an optical network, including the steps of: (a) providing each part of the network with: (i) a network interface unit, and (ii) a transceiver including: (A) transmitter imaging optics, (B) at least one transmitter optical waveguide for optically coupling the network interface unit to the transmitter imaging optics, (C) receiver imaging optics, and (D) at least one receiver optical waveguide for optically coupling the network interface unit to the receiver imaging optics; and (b) aiming the transceivers so that at least part of the optical signals emerging from the transmitter imaging optics of a first the transceiver are intercepted by the receiver imaging optics of a second the transceiver and so that at least part of the optical signals emerging from the transmitter imaging optics of the second transceiver are intercepted by the receiver imaging optics of the first transceiver.
According to the present invention there is provided a method for exchanging optical signals between two parts of an optical network, including the steps of: (a) providing each part of the network with: (i) a network interface unit, and (ii) a transceiver including: (A) transmitter imaging optics, (B) at least one transmitter optical waveguide for optically coupling the network interface unit to the transmitter imaging optics, (C) an airlink receiver, and (D) a converter unit, electrically coupled to the airlink receiver and optically coupled to the network interface unit; and (b) aiming the transceivers so that at least part of the optical signals emerging from the transmitter imaging optics of a first the transceiver are intercepted by the airlink receiver of a second the transceiver and so that at least part of the optical signals emerging from the transmitter imaging optics of the second transceiver are intercepted by the airlink receiver of the first transceiver.
The basic idea of the present invention is to eliminate the conversion of optical signals in the universal converter unit to electronic signals and then back to optical signals. Instead, the outgoing optical signals, from one network interface unit in one part of the optical communications network, are launched directly into free space and are received directly by another network interface unit in another part of the optical communications network.
To facilitate the direct exchange of optical signals between the network interface units, each network interface unit is provided with an optical transceiver, based on a transceiver unit that is used either as a transmitter unit or a receiver unit. A basic transceiver unit has an optical fiber terminating at one end of a cylindrical housing and imaging optics at the other end of the housing. The optical fiber is provided with a mechanism, such as a FC/APC, for suppressing reflections at the fiber-air interface. When the transceiver unit is used as a transmitter unit, optical signals launched from the end of the optical fiber are collimated by the imaging optics into a collimated beam. When the transceiver unit is used as a receiver unit, the imaging optics focus optical signals that they intercept onto the end of the optical fiber. Preferably, the optical fiber is a multimode optical fiber so that the beam launched from the optical fiber in transmitter mode has an adequately large divergence angle.
The transmitter units and the receiver units are used in clusters, to overcome scintillation. In a compound transmitter that includes several transmitter units, the optical fibers of the transmitter units are connected to a common input optical fiber by a splitter. In a compound receiver that includes several receiver units, the optical fibers of the receiver units are connected to a common output optical fiber by a combiner. For transmission over distances greater than several hundred meters, it is necessary to amplify the optical signals input to the transmitter, using an optical amplifier such as an erbium-doped fiber amplifier or a semiconductor fiber amplifier. In a compound transmitter, one optical amplifier may be provided for the common input optical fiber, or each transmitter unit may be provided with its own optical amplifier. In the latter case, because the input and output of an optical amplifier is via a single mode optical fiber, a mechanism such as a FC/APC is provided for coupling the single mode output of each optical amplifier to the multimode optical fiber of the respective transmitter unit.
To facilitate aiming, the transmitter and receiver units of a transceiver are aligned mutually so that all their optical axes are parallel.
The common output optical fiber of a compound receiver preferably is a multimode fiber. In case the network interface unit is designed to receive single mode optical input, the common output optical fiber is provided with a passive adapter, such as a graded index lens or a collimator, for coupling the common output optical fiber to the network interface unit. Similarly, the multimode optical fiber of a single-unit receiver is provided in such a case with a similar passive adapter.
As an alternative to all-optical reception, a transceiver of the present invention may include an airlink receiver and a fiber optic transmitter, as in the prior art universal converter unit. The transmitter of the transceiver remains all-optical.
In the application of the present invention to the exchange of DWDM signals, each network interface unit preferably includes a demultiplexer for demultiplexing the DWDM signals.
Although the examples of the present invention described herein are based on optical fibers, it is to be understood that the scope of the present invention includes optical waveguides generally. The wavelengths of the optical signals that fall within the scope of the present invention include infrared, viable, and ultraviolet wavelengths, although the preferred wavelengths are those that are commonly used for optical communication: wavelengths in the neighborhood of 850 nm, wavelengths in the neighborhood of 1330 nm and wavelengths in the neighborhood of 1550 nm.